Lithium and lithium compounds are used in a very wide range of fields such as ceramics, secondary battery materials, refrigerant adsorbents, catalysts and medicines, and have attracted attention as nuclear fusion energy resources. Also, with the commercialization of high-capacity batteries, electric vehicles and the like, the demand of lithium and lithium compounds has become a growing trend. In view of this, considering that the worldwide reserves of lithium land resources are only 2 to 9 million tons, development for securing lithium resources other than from land is desperately needed. For this, studies for effectively collecting a trace amount of lithium dissolved in an aqueous solution such as sea water, brine and a waste solution of a lithium battery are currently being conducted, and the main concern of these studies is to develop a high performance adsorbent having high selectivity and excellent adsorption and desorption performance for a lithium ion.
Conventionally, as the fruit of the above studies, a method of preparing powder which is easy to adsorb and desorb lithium using manganese oxides as a raw material by a solid state reaction method or a gel method is known in the art, and the powder prepared by the method has been used as positive electrode materials for a lithium secondary battery (Korean Patent Registration No. 10-0245808, Korean Patent Laid-Open Publication No. 10-2003-0028447, and the like), lithium adsorbent materials, and the like.
However, since using a lithium adsorbent in a powder state is accompanied by handling inconvenience, it is necessary to use it in a molded form, and for example, as disclosed in Korean Patent Laid-Open Publication No. 10-2003-9509, a method in which the powder is mixed with alumina powder, and then the mixture of the powder and alumina powder is lumped using a pore forming agent such as PVC, thereby preparing an adsorbent in a bead form, is applied to mold the powder.
Generally, a lithium adsorbent should possess essential properties such as, maintaining physical and chemical stability in an aqueous solution under various environments, and additionally, providing adsorption sites capable of securing high adsorption efficiency, maintaining high selectivity for a lithium ion so as not to adsorb elements other than lithium, and allowing an easy desorption process for recovery of lithium after adsorption.
However, in the case of preparing an adsorbent in a bead form using the conventional PVC addition method, handling is easy, but it has been reported that the adsorption sites for adsorption and desorption of lithium are decreased by about 30% or more as compared with a powder adsorbent, and thus, when it is used as a lithium adsorbent, a lithium recovery rate will be decreased.
Further, in order to overcome the above problems, Korean Laid-Open Publication No. 10-2005-0045793 discloses an ion-exchange type lithium-manganese oxide adsorbent prepared by immersing an urethane foaming agent in a lithium manganese oxide binder mixed solution, and a preparation method thereof, however, problems have been pointed out, in that since it takes a long time to adsorb lithium, the adsorbent is degenerated or deformed after a long time in the area such as a river and sea water, and particularly various pollutants such as living organisms are attached to or occur in the adsorbent, thereby significantly decreasing the lithium recovery rate with the lapse of time.
Further, Korean Patent Registration No. 10-1083256 discloses a technique to adsorb lithium by charging lithium ion mixed powder within a charger formed of nonwoven fabric, and leaving the charger in a place such as a river or sea water. However, problems are accompanied in that there is resistance to pass the sea water containing lithium ions through the pores of the nonwoven fabric, so that the sea water does not pass smoothly, and particularly, there is physical parameters such as a wave, so that the nonwoven fabric charger is folded, thereby having a serious adverse effect on an adsorption reaction, or the various pollutants are attached to or occur in the adsorbent, thereby rapidly decreasing the lithium recovery rate.